Various types of biomedical electrodes to transfer current signals between an external circuit and the skin of a person have been proposed. In order to provide good electrical contact between an electrical terminal, typically a metal element, and the skin of the person, it is customary to apply an electrolyte between the connecting points of the electrode and the skin. This electrolyte may be in the form of a gel. It can be applied directly from a gel tube or, in another form, an electrode element having a fixed electrical contact which, in turn, is an electrical connecting contact with the gel is applied to the person. The electrolyte can be absorbed, for example, in a sponge which is in contact with the contact button, or can be located in a chamber closed off by a microporous membrane so that the electrolyte, then typically a liquid, can be forced through the pores or openings closing off the chamber, for example ooze through the membrane upon application of pressure thereto.
U.S. Pat. No. 4,215,696, Bremer and Falb, describes a biomedical electrode for pressurized skin contact, and uses and applications thereof, which is disposable and includes a vaulted dome-like electrolyte-containing chamber or cavity which is bridged at its open bottom by a highly flexible, conformable and hydrophobic microporous membrane. For storage, the membrane is covered with an adhesively secured protective film which is adapted to be stripped preparatory to adhesively securing the electrode to the skin of a patient. The electrode material and shape are such that the vaulted housing can be physically distorted upon downward pressure applied thereto to force electrolyte within the chamber to diffuse through the conditioned microporous membrane into positive and low-electrical resistance contact with the skin surface of the patient. The housing maintains a positive, resilient sustained pressure of electrolyte against the skin surface due to the change in configurations of the internal volume of the chamber which contains the electrolyte upon deformation thereof, thus contributing to low-impedance electrical continuity between the skin of the patient or subject and an electrode terminal. Disruptive variations, which are objectionable in many types of electrodes applied to patients and result in change in signal strength, are minimized. Instantaneous electrical response and rapid stabilization are enhanced by the electrode in which electrolyte fluid is maintained in a continuous path through the microporous membrane against the skin.
The electrode described in the aforementioned patent has the additional feature of a ring-like transformation zone which circumscribes the housing at a height intermediate the upper and lower limits thereof, to form a mechanical discontinuity and, in essence, a snap-over or toggle action upon deformation of the housing. The zone, additionally, provides for two stable positions of the housing; one in which the housing is essentially dome-like, and another in which the housing is in compressed condition, in which fluid pressure assists electrolyte flow through the microporous membrane. This second position provides for a stable orientation of the housing with respect to the microporous membrane and establishes a constant pressure of the electrolyte against the membrane to provide a continuous conductive path between the body surface of the subject and a terminal of the electrode in contact therewith.